The manufacture of a great variety of electromagnetic and optical devices is based upon thin film technology. A succession of layers having various functionality are deposited on a planar substrate surface, one on top of another. Each is patterned in some manner, resulting in a complex three-dimensional device such as an integrated circuit. It is this technology, called metal-oxide-semiconductor (MOS) in the case of its use on doped silicon, that has enabled the computer revolution of the late 20th century, which continues today. Another example of thin film technology is the current effort to develop superconducting power transmission cables, using the coated-conductor technique. Thin films are also useful on substrates that are non-planar surfaces, such as their use as templates for oxide environmental barriers on three-dimensional objects.
There exists a wide array of crystalline oxide materials that have special or exceptional properties, and that are highly desirable as functional layers in thin-film devices. These properties include colossal magnetoresistance, ferroelectricity, superconductivity, very low thermal conductivity, and high dielectric constant, and many others.
Two major difficulties exist with the integration of these materials. First, most of these functional materials are oxides. And, as it turns out, the materials commonly or most conveniently used as a flat substrate surface are often sensitive to reaction with oxygen, such as silicon, gallium arsenide, nickel, or copper. The functional material components may be reactive with the substrate in other manners as well. Thus, it is extremely difficult to deposit highly-desirable functional oxides directly on these substrate surfaces. Barrier layers, used to block oxygen or other ionic interaction with the substrate, are used in many instances with success, although they are often complicated. Therefore more economical solutions are desirable.
The second difficulty is the need for crystalline templating. A large proportion of these functional oxides are most preferably deposited as a single-crystal-like film. That is, the crystalline material of the having a particular crystalline orientation and texture. The substrates used for deposition are frequently monocrystalline (e.g., silicon) or monocrystal-like (epitaxial, fiber-textured platinum, biaxially textured nickel), although polycrystalline surfaces are also frequently employed. If it was possible to deposit functional oxides directly on substrates, this substrate crystallinity could be used to encourage their growth in a single-crystal-like form, i.e., epitaxial growth. Epitaxial growth of functional oxides is routinely conducted, but usually only on oxide surfaces. Due to oxidation sensitivity of non-oxide substrates, epitaxial growth is prohibited in all cases but those with the most stringent growth conditions, and then for only a few specific systems.
These two difficulties can be addressed individually with reasonable success, but a method that addresses both of these difficulties concurrently is elusive. Barrier layers can be used, but are typically not single-crystal-like, being either amorphous (glassy) or polycrystalline. The growth of single-crystalline oxides directly on these substrates is exceedingly difficult.
This invention addresses this problem directly. It discloses a method, compositions, and the resulting devices for the fabrication of single-crystal-like oxide layers on oxidation-sensitive substrates, whether fabricated by the disclosed method or another. Moreover, the method is straightforward, and can be performed with far less difficulty than that encountered in direct growth of oxides on such substrates. Devices, optimally fabricated by the method, and using compositions optimal for an application, provide a templating surface that can be treated in essentially the same manner as a crystalline oxide surface. Templating is transmitted from the substrate to the film surface, and oxygen interaction with the substrate is blocked. Thus, the growth of functional oxides is made straightforward, which then can be conducted in essentially the same manner as is routinely used for their deposition on monocrystalline oxide substrates.
As an added benefit, an oxide film that the use of this method provides may also be a functional oxide in and of itself. In cases such as this, the complexity of the fabrication process is further reduced.